The invention relates to a device for testing the inflation pressure of a gas reservoir that is filled with a high-pressure gas, in particular an inert gas or an inert gas mixture to be used for inflating an airbag.
U.S. Pat. No. 4,869,097 teaches measuring of the absolute pressure of a gas, for instance helium, contained in a gas reservoir, in particular a spherical gas reservoir. An ultrasonic generator is placed on the exterior surface of the gas reservoir and ultrasonic waves are generated in a particular frequency range. These waves produce sympathetic oscillations of the gas in the reservoir, which are then measured. With the help of calibration curves, the pressure values of the gas contained in the reservoir are determined from the measured resonance frequencies. Since a significant number of successive measurements are required to obtain the pressure values corresponding to a particular resonance frequency, the known method and the known device for testing the internal pressure of cold gas inflators for airbags, for instance during the inspection of a vehicle, in which the airbag and the cold gas inflators are installed, are not suitable. A cold gas inflator filled with an inert gas, e.g. helium, for the inflation of an airbag installed in a motor vehicle, is known from U.S. Pat. No. 6,247,725.
There is provided in accordance with the present invention a device for testing the internal pressure of a gas reservoir comprising: an oscillation transmitter that can be placed on the exterior surface of the gas reservoir; an oscillation sensor that can be placed on the exterior surface of the gas reservoir; and evaluation electronics comprising a comparator, connected to the oscillation sensor and a set value transmitter that indicates the resonance frequency measured under a set internal pressure, whereby the comparator compares the resonance frequency measured by the oscillation sensor with the resonance frequency indicated by the set value transmitter, the oscillation transmitter and the oscillation sensor are integrated in a unit such that the generation and frequency measuring of the oscillations are carried out at locations on the exterior surface of the gas reservoir that are distanced from one another with respect to a longitudinal axis of the gas reservoir.